Mario Circuit (マリオサーキット, Mario Circuit) is a stage based on the course of the same name from Mario Kart 8 in Super Smash Bros. for Wii U. The stage takes place on a set of platforms that move around the track, and will stop at certain parts of the track, similar to Mute City, Port Town Aero Dive, and the 3DS-exclusive Mario Kart stage Rainbow Road. Shy Guys drive around the track, which is a reoccurring theme in the Mario Kart stages. Because of the track's antigravity effect, the road will sometimes be above or to the side of the fighters. Unlike in Mario Galaxy, fighters are not affected by the unusual gravity. The track is able to Meteor Smash anyone under it.

Mario Kart DS is the first game that allowed Shy Guys as playable characters, but only through DS Download Play. If friends wanted to play the game together, but somebody didn't have the game, they could still connect together through DS Download Play. It wasn't until Mario Kart 7 that Shy Guys were playable through normal means. In this stage, the karts are driven by Shy Guys, and the karts they drive on are the Standard Karts from that game.

If a fighter is caught by a Boss Galaga or Beetle before the stage scrolls to the section where the road is above the fighters, but breaks free as the stage scrolls to that point, they may get stuck "inside" the road and constantly be knocked back and forth, taking damage until they are blasted outside of the road.

Karts driven by Toads were planned to appear, probably similar to the Shy Guys' role in the same stage.

Though normally impossible to land on, jumping on top of the bridge while the stage is landing on the first bridge stop will KO the player.

Rarely, If the stage is played long enough (15 minutes or longer), it may restart twice, the first time being the correct looping process and the second time being as if the stage was restarted in Training Mode.

If the stage is restarted in Training Mode, all but one of the Shy Guys will disappear - the visible Shy Guy is the only one with a hitbox.